Hitherto, a heat sink board for mounting an electronic component generating heat in large amount, in particular a semiconductor component, has been basically made of a copper (Cu) material and generally formed of a one-piece plate. That type of heat sink board is inexpensive because of using a one-piece plate and has good heat radiation because of using copper as the material.
However, the copper (Cu) material has a large linear expansion coefficient of 16.6 (ppm/° C.) and faces a problem that heat generated from the mounted semiconductor component causes a crack due to thermal stress generated in a surface bonded using a solder, which has a different linear expansion coefficient. To prevent the occurrence of such a crack, it is also known to constitute a heat sink board in the form of a one-piece plate using, instead of the copper material, a copper-molybdenum (Cu—Mo) composite material that has a small linear expansion coefficient of 9.2 (ppm/° C.) and relatively good heat radiation.
In that case, however, the heat sink board is very expensive because the one-piece board is made of the Cu—Mo composite material containing a large amount of molybdenum (Mo) that has a high material cost.
Patent Document 1 (JP,A 8-186204) discloses a heat sink board comprising a mount portion made of a material having a thermal expansion coefficient close to that of a semiconductor device, and a heat radiating member made of a material having superior thermal conduction and dissipation characteristics, the mount portion and the heat radiating member being brought into an integral structure by infiltration bonding under heating.
Patent Document 2 (JP,A 6-77678) discloses a heat sink board in which a hole is formed in a predetermined position of a base material made of a nickel-iron alloy, and a heat radiating member made of a copper-based metal is embedded in the hole by screwing or pressing, thereby forming an integral board.
The heat sink board made of plural members must be held in close adhesion to a heat generating source in order to radiate heat with high efficiency. When the heat generating source is a semiconductor, for example, the semiconductor is mounted to the board by soldering, and hence the heat sink board is required to have satisfactory product accuracy, such as high flatness.
However, the former Patent Document 1 has the problem that, because of using the bonding method performed under application of heat, such as welding or brazing, the bonding accuracy is reduced due to a thermal deformation, etc., and mechanical machining is required on a soldered surface or other relevant surface after the bonding. The application of heat also makes Patent Document 1 disadvantageous in points of energy loss and material yield.
With the latter Patent Document 2 using the screwing method, the degree of close adhesion between the base material and the heat radiating member in the fastened portion is low and a sufficient effective screw length cannot be obtained in a thin plate like the heat sink board. Also, the screwing method accompanies with a risk of loosening. Further, the pressing method is disadvantageous in points of productivity and cost. In other words, because the pressing imposes deformation pressure on the heat radiating member made of a relatively soft material, desired flatness is hard to obtain and a flat-surface finishing step is required in some cases.
An object of the invention is to provide a heat sink board and a manufacturing method thereof, which can realize a high product accuracy and superior productivity.